Meanwhile Persia had become a great military empire,and, following the inevitable expansionist program induced by a slave-based economy,conquered in 546 B.C. The Ionian cities and the Greek colonies of Asia Minor.As a result a number of Greek philosophers, like Pythagoras and Xenoph-anes,abandoned their native land and moved to the prospering Greek col-onies in southern Italy. Schools of philosophy and mathematics developed at Crotona, under Pythagoras, and at Elea,under Xenophanes, Zeno, and Parmenides.